reusing yeast slurry

I recently collected approximately 500 ml of yeast slurry from a Scottish Ale. My plan has been to reuse this slurry for future brews (up next: an Irish Red). I listened to one of the Brew Strong podcasts and IIRC jamil mentions that he doesn't bother washing the yeast, especially if he's going to reuse it relatively quickly. I also checked out the yeast pitch calculator to determine how much slurry I would need for my next batch. Given the OG (1.054) and batch size (3 gallons), I only need ~50ml of slurry.

So, I poured ~100ml of the slurry into a mason jar, added some sterile water and put it in the fridge to use this weekend. However, looking at it now (pic below), it looks like 90% of the slurry is non-yeast. Am I seeing this correctly? Is only that thin, whitish layer active yeast? If so, is 50ml of the slurry going to give me enough yeast to pitch? My plan was to shake the jar up and pitch about half of it (which would give me the 50 ml that the pitch rate calculator suggests). Any advice?

Your pic definitely suggests a lot of trub with a yeast layer on top (it settles last). But, yeast is yeast and you should be able to get a starter going with what you've got - the trub will settle out once again in your starter. You are going to use a starter right?

By decanting several times during yeast washing, you are letting most of the trub settle out during each rest so you're taking mostly yeast in suspension when transferring to the next smaller vessel.

pdbreen said:

Your pic definitely suggests a lot of trub with a yeast layer on top (it settles last). But, yeast is yeast and you should be able to get a starter going with what you've got - the trub will settle out once again in your starter. You are going to use a starter right?.

Click to expand...

No. The idea is to pitch enough slurry so as not to use a starter as per the Mr. Malty pitch rate calulator. My very original idea was to throw the next brew right on top of the yeast cake, but I realized that that would be seriously overpitching, so I decided to do this the "right way" and only pitch the appropriate amount of the slurry.

Overpitching is hard to do - don't stress the amounts too much. Pitching on the cake is fine (if the recipes are compatible - same or dark/high hop after light/light hop).

But, given what you've got in the jar, I'd definitely use a starter to make sure what you're pitching is not just trub, but viable/healthy yeast.

Yeah, if the picture is showing the ~100 mL of slurry after everything has settled out, then you should be making a starter to build up the yeast count. Try to decant off most of the liquid, and when you pitch the yeast into the starter try to limit the amount of trub (dark brown stuff) that gets in.

I've been racking and sampling tonight so my guess could be a bit off, but it looks the available amount of yeast you have in that mason jar is less than or equal to the amount in a vial or propagator pack and should be grown.

To me that looks like less than 10ml of good yeast. I would really consider a small starter with that just to get some activity going with what you have.

When I have done my harvesting (I have to do one sometime today actually), I get 5 or 6 jars and 2 of them usually look like yours with the rest of them being a pretty good quantity of yeast. I haven't used any that have that much trub in there, so I really don't know how much other yeast is in the rest of that mix.

Is that the only jar you were able to save? Why are you only doing 3 gallon batches?

janzik said:

To me that looks like less than 10ml of good yeast. I would really consider a small starter with that just to get some activity going with what you have.

When I have done my harvesting (I have to do one sometime today actually), I get 5 or 6 jars and 2 of them usually look like yours with the rest of them being a pretty good quantity of yeast. I haven't used any that have that much trub in there, so I really don't know how much other yeast is in the rest of that mix.

Is that the only jar you were able to save? Why are you only doing 3 gallon batches?

Click to expand...

I have two other small jars like this one and one larger. I'll take a look at the others to see if there is more yeast in those. However, the yeast pitching calculator doesn't talk about pure yeast, but the yeast slurry, which will contain trub. There is a a slider on the calculator that allows the user to enter the % of non-yeast. It only goes up to 25%, but if I extrapolate out to 90% non-yeast, I still only get a necessary pitch rate of about 90ml of slurry.

The calculator also tells me I should use 1.1 vials of fresh yeast for this batch. So, if the amount of yeast I have in this jar is approximately equal to a single vial (as CaptYesterday suggested), then pitching the whole 100ml of slurry in this jar should be enough. This matches the slurry calculation as well.

I'm only making a 3 gallon batch because it allows me to do a more-or-less full boil, use less extract, and because I would rather make several smaller batches of different beers instead of larger batches of just a few.

I should note: I am not against making starters - I do so for all my beers when I use a fresh vial of yeast. This time however, I planned all my processes on trying this yeast slurry technique - I made a Scottish ale, am now going to make an Irish Red with the slurry, and will then use slurry from this same yeast for a Stout, and then probably a Barleywine.

So, I am trying to get this to work with the slurry and without a starter since that was my original intent.

This may not work for you (and it's too late for this one) but FWIW here's what I do. I almost always wash the yeast and save 2-3 mason jars and then immediately pitch the rest into a new brew, the new brew always has some gravity to it (1.060 or higher). So I plan my 'next' brew for the day (or two) after I will be racking the first (yeast wash) brew:

Make wash kit beforehand (boil: water, 2 qt container, and 2-3 half-pint mason jars together; fill all containers with boiled water; seal and let cool).
Rack as much beer off the cake as possible.
Add 2 qt boiled/cooled water from the 2 qt container to carboy (leave mason jars full of water), keep the 2 qt container as sanitary as possible.
Shake/agitate well, then let sit for about 20 minutes.
Carefully/slowly pour off to fill the 2 qt sanitized container and seal, you should get almost no trub (actually you should get NO trub at all).
Let settle overnight (minimum).
Decant about 2/3 of the liquid, then shake it all up well.
Discard water from mason jars (or use it for something else) and pour loose slurry into the 2-3 mason jars and seal, pour the rest into your fermenter full of wort.

I always try to keep the water at the same temp as the initial fermentation so lager yeasts stay cold and ale yeasts stay room-ish temp.

This way you get a few mason jars of washed yeast (and it should be at least 50mL packed into the bottom...often closer to 100mL) and you get to pitch at a high rate into a new brew but you're not overpitching (at least not by much).

You've got a lot of crud in there, but that bottom portion has good yeast mixed in with it. Shake up the yeast with some sterile water, let settle for 10 to 15 minutes and pour off the liquid to another container. Do this a couple times and you should end up with some clean yeast and less trub.

jamilz said:

You've got a lot of crud in there, but that bottom portion has good yeast mixed in with it. Shake up the yeast with some sterile water, let settle for 10 to 15 minutes and pour off the liquid to another container. Do this a couple times and you should end up with some clean yeast and less trub.

Click to expand...

As from my original reply, I usually get 2 or so of these per 5 or 6 mason jars I collect. How many rewashings for something that likes like the OP's pic is worth it before you risk contamination? I guess it doesn't matter too much as long as you keep a sanitary environment?

For the 3 or 4 good mason jars that I get relatively clean on the first try, Should I just set Mr Malty to 4.5 Thick Yeast, leaving the Non Yeast as the default and estimate my pitching quantity from there?

(My example is for my 1.068 IPA, that I'm going to brew again with the harvested yeast)... If a 1.068 5.5 gal batch harvested today would require 70ml of thick yeast, wouldn't making a starter for my batch that I brew next week or the week after, or whenever be considered overpitching? Should I technically only pitch 70ml? (which to me probably wont happen and I'll just pitch the whole starter anyway)

Today I'm harvesting from a harvest, So I guess this would be a second (or third?) generation yeast. Is there anyway to take into account the viability between generations?

OK, I think I've realized my error and confusion. I had a small email back and forth with Jamil that I think has helped clear things up for me.

I had assumed that "yeast slurry" and trub were the same thing. I realize now, that the "yeast slurry" is the layer of viable yeast - the creamy white layer in the original photo. So when the pitch rate calculator says that I need ~50ml of slurry, it means I need ~50ml of that creamy white yeast layer. In that layer, some percentage of non-yeast is found and that is where the non-yeast % value (up to 25%) comes into play.

I am going to rerinse all the yeast I collected and get rid of the trub and then see how much slurry I have. I imagine I'll have ~50ml total, which will be enough to pitch directly for my next batch.

update: I rerinsed the jars of yeast I collected and ended up with 4 jars like the ones below. I estimated each jar contains 30ml or so of good yeast, so I pitched 2 jars into my latest batch. Seems to have worked great as fermentation started in less than 12 hours.

pitch it? why not just drink it?! mmm...looks delicious.